The Prostate Cancer Prevention Trial (PCPT) is a double-blinded, phase III study of the safety and efficacy of finasteride in the prevention of prostate cancer. PCPT is a chemoprevention trial. The study is funded by the National Cancer Institute through the Division of Cancer Prevention and Control. The primary objective of the Prostate Cancer Prevention Trial is to test the difference in the biopsy-proven prevalence of carcinoma of the prostate between a group of participants treated with finasteride and a group treated with placebo for seven years. The secondary objectives of the study are 1) to assess the effect of finasteride on the stage and grade of carcinoma of the prostate at the time of diagnosis, 2) to assess the toxicity and side effects of finasteride when administered on a long-term basis, 3) to estimate the difference in the total and prostate-cancer specific mortality between men treated with finasteride and those treated with placebo, 4) to estimate the difference in incidence and severity of benign prostatic hyperplasia between men treated with finasteride and those treated with placebo, 5) to estimate the sensitivity, specificity and predictive values of digital rectal examination (DRE), Prostate Specific Antigen (PSA), and PSA + DRE as screening tests for the detection of prostate cancer, and to estimate the effect of long-term finasteride treatment on these screening parameters, and 6) to assess the effect of long-term treatment with finasteride on the participants' self-report of urinary and sexual function symptoms and other Quality of Life dimensions.